Ice dam risk in St. Charles, IL
How often ice dams form in St. Charles
13.4 dam days a winter
Moderate risk. On an ordinary house in St. Charles, conditions for an ice dam come on about 13.4 days in a normal winter, mostly in January and February.
St. Charles averages 28 inches of snow a year and about 42 days with snow on the ground. Most of it comes and goes within a few days. The conditions that make a dam need all three at once: snow, cold at the eave and heat above it.
What your attic does to that number in St. Charles
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 6.8 | Moderate |
| Typical, some insulation, not air-sealed | 13.4 | Moderate |
| Older or poorly insulated, warm attic | 21.8 | High |
Sealing and insulating a typical attic takes out about 6.7 days a winter here. It does not move the risk band, but it shortens every dam. An older house with a warm attic should expect closer to 21.8 days.
Preventing ice dams on a St. Charles roof
- Air-seal the attic floor: the gaps around the hatch, light fixtures, plumbing stacks and the top plates of interior walls. This is the fix that removes the cause, and it usually costs less than a season of contractor ice removal.
- Rake the bottom three or four feet of roof after any storm that leaves more than about six inches, from the ground with a roof rake.
Which to spend on first: air sealing or heat cable.
St. Charles winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 9.1 | 16.4 | 6.0 |
| February | 7.9 | 11.3 | 3.6 |
| March | 2.6 | 3.5 | 0.7 |
| April | 0.6 | 0.3 | 0.0 |
| November | 1.3 | 1.0 | 0.2 |
| December | 6.4 | 9.5 | 2.9 |
St. Charles next to nearby towns
St. Charles ranks 89 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Geneva, IL 3 mi, 13.4 days
- South Elgin, IL 5 mi, 14.7 days
- West Chicago, IL 5 mi, 13.4 days
- Batavia, IL 5 mi, 13.4 days
- Campton Hills, IL 6 mi, 14.7 days
Where these numbers come from
NOAA 1991–2020 climate normals from Aurora, 9.6 miles from St. Charles. A dam day is a day with snow on the roof and freezing at the eave while heat or sun melts the snow above it. This describes a normal winter, not this one.